1. Field of the Invention
The present invention relates to an ATM (Asynchronous Transfer Mode) switch, and more particularly to an ATM switch which performs cell rate shaping of changing the output rate dynamically for each virtual channel (VC) and for each virtual path (VP) in response to a stored amounts of cells.
2. Description of the Related Art
Conventionally, an ATM switch has a cell rate shaping function on the output cell buffer side and output cells with the peak cell rate controlled for each virtual channel or virtual path.
It is sometimes desired to achieve minimum cell rate assurance of each virtual channel (VC) of a virtual path (VP) and peak cell rate shaping of the virtual path and each virtual channel of the virtual path on condition of Σ (VCMCR)≦VPPCR≦Σ (VCPCR) where Σ (VCP CR) is the peak cell rate total value 20 of the virtual channels in the virtual path, Σ (VCMCR) is the minimum cell rate total value of the virtual channels in the virtual path, and VPPCR is the peak cell rate of the virtual path. However, with a conventional shaper, if cell rate shaping is performed for each virtual path, then it is impossible to realize minimum cell rate assurance and peak cell rate shaping of each virtual channel in a virtual path.
Also it seems a possible method to use two conventional shapers connected in two stages such that the peak cell rate is controlled for each virtual channel in the preceding stage whereas the peak cell rate is controlled for each virtual path in the succeeding stage. However, in order to realize the minimum cell rate assurance for each virtual channel in both of the two stages, complicated feedback control to the input cell buffer side is required, and even if the minimum cell rate assurance is realized, a high cost is required disadvantageously.